Screw conveyors are commonly used as a means for removing materials from a bin or hopper and usually employ a shroud or casing extending from the intake opening of the hopper and enclosing the feeder screw to assure consistent flow control.
In resource recovery systems, for example, a screw conveyor is utilized to remove shredded materials from a supply hopper to the interior of a rotary air drum classifier which separates the mixed materials into light and heavy materials. Such a system is disclosed in U.S. Patent application Ser. No. 580,373, filed May 22, 1975, by the assignee of the present invention. In such a system a cylindrical casing or housing is fixed at one end to the hopper and its other end projects into the interior of a hollow drum which is mounted with its longitudinal axis disposed at an angle to the horizontal and which is made to rotate about its axis to cause heavy materials falling from the conveyor to move progressively downwardly within the drum and to eventually fall out of the lower end thereof, while light materials become entrained in a high velocity flow of air which carries the light materials out of the upper end of the drum.
It is well known that the materials being transported by the screw conveyor often contain substantial amounts of water. This is especially true in commercial waste recovery systems which process materials including amounts of garbage which have a relatively high water content. Consequently as the wet materials are forced by the screw through the duct they tend to be compressed or compacted to such an extent that they will eventually emerge from the exit end of the conveyor as relatively large agglomerations or lumps wherein various parts or materials adhere together by the action of the water. In a materials separation system, such as a drum classifier, it sometimes happens that these agglomerations, unless broken up, will be removed with the heavy materials although the constituents of the agglomerations would otherwise be removed with the light materials.
Apparatus of this character will work well when completely dry materials are used. Therefore, attempts to heat and consequently dry such wet materials while simultaneously aerating them have been attempted. One such attempt is disclosed in U.S. application Ser. No. 580,374, filed May 22, 1975. However, it is not always convenient to supply heat to the apparatus.